Interaction between intermediate/deep-water masses and the sedimentation in a mid-slope canyon off Argentina/Uruguay during the last 25 kyr

Submarine canyons are major conduits of sediment transport to the deep ocean. Many canyons have a connection to the shelf. However, in the last decades an increasing number of canyons reveal a mid slope canyon head, such as... [ view full abstract ]

Submarine canyons are major conduits of sediment transport to the deep ocean. Many canyons have a connection to the shelf. However, in the last decades an increasing number of canyons reveal a mid slope canyon head, such as the Mar del Plata Canyon at the Argentina/Uruguay margin that is intensely shaped by contour currents. The Mar del Plata canyon crosses all intermediate- and deep water masses of the region. The sedimentary record of gravity cores from inside the canyon includes turbidite beds and contourite deposits fed by the northward flowing Antarctic Intermediate Water (AAIW).

Despite the influence of the corrosive southern sourced Deep Waters (SSDW) deeper than 3000 m water depth we were able to produce a high resolution Holocene to Last Glacial record using 8 AMS-14C ages and Ca/Fe XRF records for correlation of cores. Methodological approaches of our study include Xray-radiographs, elemental ratios, magnetic susceptibility and grain size distribution. We focus on the terrigenous sortable silt (SS) mean grain size and percentage in the background sediments to assess relative bottom current strength.

In general, SS values support magnetic susceptibility and Zr/Al down core ratios. At the proximal core site (GeoB13861) the deglacial section reveals several turbidite intercalations. High SS values and Zr/Al ratios in the background sediments indicate stronger AAIW flow. This may have increased sediment deposition in the upper canyon and periodically released turbidity currents. In all cores a consistent pattern of turbidite occurrence is observed. High turbidite frequency is registered during the Last Glacial Maximum (LGM) and the last deglacial period whereas no turbidites are found in the Holocene sections. Thickness of turbidites decreases downward along the thalweg. The LGM section of the levee core on the distal northern canyon side (GeoB13823) displays several over-spill turbidites. We assume that at this deep position the SSDW flow may have shifted the suspended sediment cloud onto the Necochea Terrace.

References

Voigt I, Henrich R, Preu B, Piola AR, Hanebuth TJJ, Schwenk T, Chiessi CM (2013) A submarine canyon as climatic archive – Interaction of the Antarctic Intermediate Water with the Mar del Plata Canyon (Southwest Atlantic). Marine Geology, 341: 46-57.